Replacing row in matrix with previous row depending on condition
4 views (last 30 days)
Show older comments
Hi
Say I have a matrix:
A=[2,5,3;5,8,2;1,-2,5]
If a value in any of the rows are -2 the whole row should be replaced by the previous row.
So the result would be:
A=[2,5,3;5,8,2;5,8,1]
The matrix consists of 1 million rows, so I'm looking for the fastest method.
0 Comments
Accepted Answer
the cyclist
on 19 Jun 2020
Here is one way:
while any(A(:)==-2)
rowToReplace = find(any(A==-2,2));
A(rowToReplace,:) = A(rowToReplace-1,:);
end
This solution could probably made faster by using only logical indices, without the find command, but I felt lazy.
2 Comments
the cyclist
on 19 Jun 2020
This is a little faster, in limited testing:
while any(A(:)==-2)
rowToReplace = any(A==-2,2);
A(rowToReplace,:) = A([rowToReplace(2:end); false],:);
end
The optimized version might depend on the pattern of -2's in the array.
More Answers (1)
David Hill
on 19 Jun 2020
If you have consecutive rows containing -2, you will have to repeat until all the -2 rows have been replaced if that is your goal
[a,~]=find(A==-2);
a=unique(a);
A(a,:)=A(a-1,:);
See Also
Categories
Find more on Matrix Indexing in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!